1. Field of the Invention
The present invention relates generally to switchgear cabinetry for use with circuit breakers and, more particularly, to a switchgear cabinet having a door that is configured to withstand the explosive forces of the gases produced during arcing faults.
2. Description of the Related Art
Metal-clad switchgear is desirably employed for medium voltage switchgear operating at voltages from 5 to 38KV, and for even higher voltages. In some switchgear configurations, circuit breakers and/or other elements of the switchgear are housed in metal enclosures and are removable. Draw-out apparatuses can be used to move the circuit breakers or other elements between a disconnect position in which the primary contacts between the circuit breaker and the switchgear cabinet are fully disengaged and a connect position in which the primary contacts are fully engaged. A hoist typically is often used to mount the circuit breaker on the draw-out apparatus and to remove it therefrom. Other types of switchgear are used in conjunction with circuit breakers that are mounted on casters and are rolled along a floor or on rails laid on the floor and directly into the switchgear cabinet instead of being mounted on draw-out apparatuses.
Such switchgear typically includes a variety of auxiliary devices and related control circuitry included potential transformers, current transformers, and fuse drawer components. The design of such metal-clad switchgear typically concentrates on structures that reduce the possibility of arcing faults within the enclosure. For instance, all primary elements such as breakers, voltage transformers, and control power transformers have disconnect means with isolating shutters to establish isolation from the high voltage sources.
All operations on breakers, potential transformers, and current transformers in the metal-clad switchgear are preferably performed with the compartment doors closed for operator safety. The front door may be interlocked with the shutter assembly to reduce the chance of accidental opening of the front door during partial levering-in of the breaker or other equipment.
The switchgear enclosures that contain the primary elements of the power distribution system such as the circuit breaker compartment, the main bus compartment, and the cable compartment have been compartmentalized and grounded for maximum isolation and confinement. Within these compartments, all live parts where possible are fully insulated to reduce the likelihood of an arcing fault.
Although arcing faults are rare, injuries from arcing faults in metal-clad switchgear nevertheless may occur. Arcing faults are very destructive due to the high energy levels reached within a confined compartment. The structural containment must be adequate to substantially prevent the escape of arcing products and hot gases from the faulted compartment. Burns can result if operating personnel are in close proximity with the faulted switchgear.
Arcing faults can occur within a switchgear compartment as a result of insulation failure or human error. The pressure from an electric arc is developed from two sources: the expansion of the metal by boiling, and the heating of air by the arc energy. Copper expands by a factor of 67,000 times in vaporizing. This accounts for the expulsion of near-vaporized droplets of molten metal from the arc. One test has shown that droplets could be propelled up to ten feet. The pressure also generates and directs plasma outward from the arc for distances proportional to the arc energy. One cubic inch of copper vaporizes into 1.44 cubic yards of vapor. The air in the arc stream expands due to its being heated from ambient temperature to the temperature of the arc (approximately 35,000xc2x0 F.).
All of this happens within the at least first half cycle of the fault and results in a sudden and dramatic increase in pressure inside the compartment. Such elevated pressure acting on the door of the faulted compartment can potentially generate sufficient force to blow the door off the cabinet. Such switchgear thus must be designed to not only reduce the likelihood of arcing but also to contain and withstand the pressures that are created during such arcing in order to prevent personal injury.
Switchgear can be designed in numerous ways to retain the door thereon and to resist the door from being blown open or off during an arcing fault. Such doors typically have included overlapping or interlocking members around the perimeter of the door that operate as interference structures which interfere with movement of the door away from the frame of the switchgear cabinet and thus help to secure the door to the frame.
Special problems are introduced, however, for switchgear cabinetry that is used in conjunction with caster-mounted circuit breakers that are rolled on floor directly into the switchgear cabinet. The casters of such circuit breakers cannot easily be rolled over interlocking or overlapping structures that are disposed at the lower end of a cavity and that cooperate with structures disposed at the bottom end of the door. It is thus desired to provide an arc-resistant switchgear cabinet having retention structures at the bottom end thereof that secure the bottom of the door to the frame yet do not interfere, or at most only nominally interfere, with the operation of rolling the circuit breaker into and out of the cavity on casters.
In view of the foregoing, an arc-resistant switchgear cabinet includes a frame disposed on a floor and a door movably mounted on the frame. The frame includes a floor plate that is disposed against the floor and that includes a plurality of pins extending vertically upward from the floor plate. The door includes a plurality of corresponding receptacles into which the pins are received when the door is in a secured position. The pins in the receptacles resist the lower end of the door from moving in a horizontal direction away from the frame in the event of an arcing fault. A pair of bolts additionally fasten the lower corners of the door to the frame. The switchgear cabinet further includes interlocking tabs formed on the frame and on the door that overlap one another when the door is in the secured position.
It is thus an objective of the present invention to provide an arc-resistant switchgear cabinet having a door that is resistant to being blown open in the event of an arcing fault.
Another objective of the present invention is to provide an arc resistant switchgear cabinet formed with a cavity, in which a circuit breaker mounted on casters can be rolled from a floor into the cavity substantially free of interference with the retention structures that retain a door of the switchgear cabinet in a secured position during operation of the circuit breaker.
Another objective of the present invention is to provide an arc-resistant switchgear cabinet that is pivotable between an open position and a closed position, and that is translatable between the closed position and a secured position, with pins on a floor plate of the switchgear cabinet engaging receptacles in the door when the door is translated from the closed position to the secured position.
Another objective of the present invention is to provide an arc-resistant switchgear cabinet having a door that employs both interference structures as well as fasteners to retain the door in a secured position on the switchgear cabinet.
An aspect of the present invention is to provide an arc-resistant switchgear cabinet structured to be mounted on a floor, in which the general nature of the arc-resistant switchgear cabinet can be stated as including a frame that includes a floor plate, the floor plate being structured to engage the floor, a door mounted on the frame, the door being movable between an open position and a secured position, at least a first pin mounted on one of the door and the floor plate, the at least first pin being oriented substantially perpendicular to the floor plate, and the other of the door and the floor plate being formed with at least a first receptacle, the at least first pin being removably engageable in the at least first receptacle, the at least first pin being at least partially disposed in the at least first receptacle when the door is in the secured position, the at least first pin being disengaged from the at least first receptacle when the door is in the open position.
The door of the arc-resistant switchgear cabinet may include at least a first fastener structured to engage the door with the frame. Additionally, the door may be translatable between a closed position and the secured position, the closed position of the door being operationally interposed between the open position and the secured position of the door.
The frame may include a plurality of first tabs alternating with a plurality of first notches, and the door may include a plurality of second tabs alternating with a plurality of second notches, with the first tabs passing through the second notches and the second tabs passing through the first notches when the door is moved between the open and closed positions, and with the first tabs at least partially overlapping the second tabs when the door is in the secured position.
The arc-resistant switchgear cabinet may include a hinge extending between the frame and the door, with the door being pivotable on the hinge between the open position and the closed position.
The arc-resistant switchgear cabinet may also includes a closing mechanism operatively extending between the door and the frame and being structured to translate the door from the closed position to the secured position.
The arc-resistant switchgear cabinet may also include at least a first fastener extending between the door and the frame and being structured to engage the door with the frame.